There is probably no other occasion in Star Trek Voyager
that shows us as many different alien races as the spectators in VOY:
"Tsunkatse".

The Tsunkatse games take place on the Norcadian homeworld,
or that is what the people think who come there to watch them. The actual arena
is located on a ship and transmitted to a holographic projector on the
homeworld. Besides the crew of Voyager we can see several members of Penk's race
with two characteristic forehead bulges. They are among his aides as well as in
the audience. Though never explicitly mentioned, these were obviously meant to
be the Norcadians at the time "Tsunkatse" was being produced, although
it will be unmistakably stated in two later episodes that actually Mezoti
is Norcadian.

Penk
VOY: "Tsunkatse"

Three spectators of Penk's race
VOY: "Tsunkatse"

Analysis

Most of the spectators belong to various other alien races. And it seems none of
their make-ups is new. The following images depict and identify most of the
alien visitors that can be seen in the episode.

Collage #1 Here we can see the following alien make-ups:

A Tygarian. The species first appeared and received its
name in DS9: "The Homecoming" but could be seen no less than 35
more times as a background alien on DS9.

Two Ankari. They appeared in VOY: "Equinox",
where it was also implicitly established that they must possess a very
advanced propulsion system that might allow them to visit the Tsunkatse
arena. The Ankari make-up is quite similar to that of the Tygarian. It is
probably no coincidence that the two are standing side by side. They are apparently
meant to be the same species here.

DS9 alien #1. This unnamed alien with his long face was
first seen in DS9: "Armageddon Game" and showed up ten more times,
mostly on the promenade.

DS9 alien #2. This species with a triangular face first
appeared as soon as in the second season. In DS9:
"Cardassians" and "Sanctuary" we could see these aliens
with big gray hats that were omitted for the following nine appearances.

A healthy Vidiian. This is the healthy look of the race
as seen on Danara Pel in VOY: "Lifesigns", as opposed to the
patchwork faces of the Vidiians with the phage. Although it is unlikely that
the spectator could really be a Vidiian, it would confirm Kurros' statement
that the Think Tank eventually cured the Vidiian phage.

A Voth. The vastly advanced descendents of Earth
dinosaurs seen in VOY: "Distant Origin". Although the Voth do have
transwarp drive and hence would be able to bridge the vast distance to the
Norcadian homeworld, they consider non-reptilian humanoids inferior and
wouldn't really like to watch such a primitive fight. We could want to
explain the presence of the Voth with him performing a cultural study, but
we can see him cheer just likely everyone else does.

A Boslic. This female make-up could be seen in three
DS9 episodes, and the look is considerably different than that of the men of
the same species. While the real-world reason for the existence
of two make-ups is likely just inattention, it may qualify as a quite
definite sexual dimorphism. Anyway, while the
original Boslic woman has purple hair, it may be brown on the Tsunkatse
spectator.

Collage #1

Collage #2
This collage allows to identify
the following additional alien make-ups:

A hostile alien from VOY: "Latent Image". We
could see them only in a flashback in the episode as they boarded a shuttle,
the event dating back 18 months, tens of thousands of light years from the
Norcadian homeworld.

DS9 "tailhead" alien. This fellow appeared as
soon as in DS9: "Emissary" and TNG: "Tapestry" and in 13
more episodes. The wrinkles in the face appear to have been toned down for
"Tsunkatse" but the tail is definitely there, as the reverse angle
of the scene proves. Purportedly the quite fitting name "tailhead"
was used by Michael Westmore behind the scenes.

A Reptohumanoid. They could be seen in VOY:
"Parturition", as early as in the second season of the series.

A member of Abbadon's race. The make-up (from VOY:
"Alice") appears to have been slightly modified. Yet, the
spectator could be well another member of this race that was encountered
earlier in the same season.

A member of Yost's race (Renovation Team Nova). Exactly
as seen in VOY: "Gravity".

A combination of Torat's race and the Evora. The
make-up visible in "Tsunkatse" is composed of Torat's face (VOY:
"Counterpoint") and the back of the head of the Evora ("Star
Trek: Insurrection"). Interestingly, in VOY: "Survival
Instinct", on the space station, we could still see both of them as
individual make-ups.

Collage #2

Collage #3
This one depicts still more
alien make-ups:

A Kressari. After the first appearance of this race in
DS9: "The Circle" we can see more members no less than 27 times as
background aliens.

A Parada. The race first appeared in DS9:
"Whispers" (then still in a bad light, literally and
figuratively). After that we could see them 24 more times on DS9.

A member of the "Swarm". These nasty aliens
showed up in VOY: "The Swarm". We could also see this species in
Seven's nightmares in VOY: "Infinite Regress". Obviously members
of the Swarm have been assimilated by the Borg.

Collage #3

Collage #4
This collage has has one more alien
make-up:

A Kobheerian. It is definitely a Kobheerian, as first
seen in DS9: "Dramatis Personae", not a Dopterian, although it is
easy to confuse the two races.

Collage #4

Conclusion

So we have
seen almost all of the spectators before, many of them tens of thousands of
light years away in the Delta Quadrant or even in the Alpha and Beta Quadrants.
It is clear that none of these could possibly attend the Tsunkatse show on the
Norcadian homeworld, unless they had advanced propulsion systems such as the
Voth or the Ankari. But even though we might be able to explain away the
presence of single races that normally shouldn't be there, there is no way to
justify their amassment. Ultimately we were are supposed to perceive the
audience as a colorful bunch of aliens, and not as members of particular known
races.